In a communication system complying with LTE/LTE-advanced (to be referred to as LTE collectively hereinafter), DRX control is adopted for the purpose of battery saving of a user apparatus UE (refer to non-patent document 1).
In DRX control, a user apparatus UE that is RRC-connected (RRC connected UE) is managed with two states that are an Active state and an Inactive state.
In an Active state, the user apparatus UE monitors a DL control channel (PDCCH) so as to report feedback information (CSI: Channel State Information) or SRS (Sounding reference symbol) to a base station eNB.
On the other hand, in an Inactive state, the user apparatus UE does not monitor the DL control channel, and does not report feedback information and the like. By such a control, battery saving is realized.
In DRX control, for example, as shown in FIG. 1 and FIG. 2, transition between an Active state and an Inactive state is performed.
FIG. 1 is a diagram showing an example of transition by a DRX Inactivity Timer. The DRX Inactivity Timer starts after receiving a PDCCH indicating that there is data, and after that, when the DRX Inactivity Timer expires without receiving a PDCCH, the state changes to the DRX state. In the example of FIG. 1, after receiving the last PDCCH, the DRX Inactivity Timer expires so that the state becomes the DRX state, then, an Active state and an Inactive state repeat at a DRX cycle. Also, in each DRX cycle, an Active period defined by an “on duration timer” is called on duration.
FIG. 2 is a diagram showing an example of transition by a DRX command MAC control Element (DRX MAC CE). As shown in FIG. 2, the DRX MAC CE forcibly stops the DRX Inactivity Timer so as to make the user apparatus UE to enter the DRX state even before expiration of the DRX Inactivity Timer.